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Old Nov 18, 2011, 11:59 AM
Tim Green is offline
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I think too many of us, succumb to what we learned in school - Bernoulli - and it's hard to shake that off. It's in our blood. Even in the face of experiments, showing it's the air that's expelled by a system, that determines lift. I don't see any of you having a hard time with this, if you weren't first taught the wrong thing. I went throught it too. But the Bernoulli explanations just weren't clicking. Too many unexplained facts (such as choppers throw down tremendous amounts of air, such as when you redirect that air, you change the lift vector). So, I kept at it. Now I'm trying to convert others. It's been hard to do. So, I largely keep to experiments, as these are incontrovertible, whereas long verbal explanations, well, they're long verbal explanations, subject to interpretation, and not much fun. Experiments are fun though.
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Old Nov 18, 2011, 12:08 PM
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greg
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Originally Posted by Tim Green View Post
You said it both ways - and you cannot have it both ways. Either it's relevant, or it's not. And so far, experiments prove it's always relevant. Always - an object moves opposite the direction of any air it exhausts.


Someone took a box. Cut three holes in the front, and put the box on wheels. Then they took a fan, attached it to the middle hole in the box, such that the fan was blowing into the box. Bernoullists would claim that the box would move forward, pulled by the fan. But the experiment showed the box moving backward, propelled by the air it was expelling through the other two holes.

Block the two exhaust holes, and the box doesn't move at all. Bernoulli alone, cannot move the box.

This experiment, plus the chopper with the plate - prove Bernoulli ain't lifting nuttin.

No one on this forum, has come up with a chopper experiment, showing Bernoulli only lift, or any Bernoulli lift. But we can come up with an infinite number of experiments showing the following ...

A. No have lift without throwing air down.
B. The direction of an object's thrust vector is determined by the direction of the air leaving the object. (not the direction of any props, rotors, fans, etc., moving air into the object)

And rotors are wings - which is why fans and choppers make this work so easy - if you don't disregard the experimental data.
i thought i agreed with you
Old Nov 18, 2011, 12:10 PM
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...
Last edited by Steve Anderson; Sep 30, 2014 at 07:13 PM.
Old Nov 18, 2011, 12:15 PM
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Too many unexplained facts
Like the ones I have been asking you about and you have not answered for me (maybe you don't have an answer, I don't know) regarding the air pressure "sucking" the air causing the acceleration. I, like you, look at an explanation for something and see something missing, and want to know why.

Quote:
So, I largely keep to experiments, as these are incontrovertible, whereas long verbal explanations, well, they're long verbal explanations, subject to interpretation, and not much fun. Experiments are fun though.
Seems like you are wrong, your experiments have been interpreted 2 different ways, and have caused lots of "controversy" on this forum.

Well, as I can not get a straight answer out of you, and you refuse to actually discuss anything other than your idea....well, good luck, have fun.

I tried to understand your idea this time, you simply blocked out my attempts to see your point of view.
Old Nov 18, 2011, 12:43 PM
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And in the other case, the chopper doesn't deflect the airflow, due to the plate being folded.
But the box blocks the flow in the same way as the plate....meaning the paths the air particles take is the same in both cases. If you can't agree to this then I can't reason with you.
Old Nov 18, 2011, 03:35 PM
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Bernoulli in my Brain!


I did a Science Project in Middle School (1979) about "How a plane flys". Bernoulli has been in my mind ever since. However since I have been flying RC planes for the last 2 seasons, I kept wondering "How does that explain a plane flying upside down"? Not to mention symetrical airfoils! You have my attention!

VP
Last edited by Victory Pete; Nov 18, 2011 at 05:43 PM.
Old Nov 18, 2011, 03:40 PM
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Newton tells us F=MA Translated for flying, Lift=mass of air x acceleration of that mass in a downward direction.
Old Nov 18, 2011, 07:05 PM
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in herks' box, does the box move due to the outflow of air (pressing against what?), or because there is increased pressure inside the box and there is less surface for the air to press against on the side with the openings (including the fan)? would the box move differently if the openings were bigger/smaller (than the area of the fan)?

hasn't someone already said you have to consider all the forces affecting (contacting) the system?
Old Nov 18, 2011, 07:41 PM
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WoW, I give up. I was going to draw some pretty pictures showing the air flow from the copter blades and how it bends when it reaches either the plate or the box (or the floor) but this (Censored) idiot is so ignorant and at the same time sure if his misinformation that there is no proving *anything* that differs with his illusions.
Old Nov 18, 2011, 09:19 PM
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i thought i agreed with you
Whoops (oops).
Old Nov 18, 2011, 09:26 PM
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Originally Posted by ciurpita View Post
in herks' box, does the box move due to the outflow of air (pressing against what?), or because there is increased pressure inside the box and there is less surface for the air to press against on the side with the openings (including the fan)? would the box move differently if the openings were bigger/smaller (than the area of the fan)?

hasn't someone already said you have to consider all the forces affecting (contacting) the system?
If you put the exit holes somewhere else, the box moves opposite the side the holes are on.

Proving the box moves in response the the air it's expelling. Not the air it's taking in.
Old Nov 18, 2011, 09:29 PM
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But the box blocks the flow in the same way as the plate....meaning the paths the air particles take is the same in both cases. If you can't agree to this then I can't reason with you.
Box isn't attached - plate is.
Last edited by Tim Green; Nov 18, 2011 at 09:39 PM.
Old Nov 18, 2011, 09:30 PM
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But the box blocks the flow in the same way as the plate....meaning the paths the air particles take is the same in both cases. If you can't agree to this then I can't reason with you.
Box is irrelevant - this experiment works the same if you run the experiment on a grating.
Old Nov 18, 2011, 09:32 PM
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Seems like you are wrong, your experiments have been interpreted 2 different ways, and have caused lots of "controversy" on this forum.
Oh well - some people cannot let go of Bernoulli - like an old friend.
Old Nov 18, 2011, 09:33 PM
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Tim,
You need to re-read this thread from 2003 that you were involved in. Note post #24 by Mark Drela.

https://www.rcgroups.com/forums/showthread.php?t=135318
Don't see your point.


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